Various reactors, such as a vessel type reactor, a tubular reactor, a tower type reactor, a fluidized bed type reactor and a special reactor, are generally known as reaction apparatuses.
These reactors are properly selected according to the type of reaction, properties of the desired products, etc. For example, if the aimed reaction is a polymerization reaction, a vessel type reactor or a fluidized bed type reactor is usually used as the polymerization reactor.
When the vessel type reactor is used as the polymerization reactor, liquid phase polymerization using a solvent, such as solution (homogeneous) polymerization or slurry polymerization, is generally carried out. The liquid phase polymerization is advantageous in that polymers of relatively high qualities can be obtained and there are few restrictions on the properties of the resulting polymers and the operating conditions.
In the liquid phase polymerization using the vessel type reactor, however, the resulting polymer is dissolved or suspended in a polymerization solvent while stirring to form a polymer liquid (polymer solution or suspension), such that with an increase of in the viscosity of the polymer liquid, the power requirement are increased for stirring the polymer liquid. Especially in the industrial production of high-viscosity polymer liquids, huge stirring equipment is necessary and the stirring energy tends to become enormous.
In the liquid phase polymerization, further, the resulting polymer must be separated from the solvent after polymerization. Therefore, equipment and energy for the separation are further required, and in some cases, equipment for purifying the solvent must be furthermore provided.
When the fluidized bed type reactor is used as the polymerization reactor, the polymerization is carried out while solids (catalyst, resulting polymer) are fluidized by means of a gas medium to form a fluidized bed. Therefore, removal of the medium is usually unnecessary, and polymers can be produced at low costs. However, the gas linear velocity must be controlled to maintain the fluidized bed. Besides, in such polymerization that the quantity of reaction heat is large, the heat exchange quantity sometimes restricts the polymerization, or in such polymerization that the resulting polymer has a low melting point, formation of a fluidized bed occasionally becomes impossible. Thus, the operating conditions are frequently restricted.
In the use of the vessel type reactor or the fluidized bed type reactor, it is difficult to add raw materials at a suitable position of the reactor depending on the progress of the polymerization so as to control properties of the resulting polymer. Therefore, plural reactors are usually employed to obtain polymers of desired properties.
Polymerization reactions using a tubular reactor as the polymerization reactor are also known, for example, a high-pressure polymerization reaction (e.g., for producing high-pressure polyethylene) in which a monomer gas compressed under an elevated pressure to a supercritical fluid is fed to the tubular reactor (reaction tube) where the reaction takes place in a substantially homogeneous liquid phase system, and a homogeneous or slurry polymerization reaction using a liquid medium. It is also known that the tubular reactor is used as an apparatus for controlling the properties of the resulting polymer after the vessel type reactor or the fluidized bed type reactor.
In the conventional polymerization processes using a tubular reactor, however, the viscosity (or concentration) of the polymer liquid which can be transported (carried) in the reaction tube tends to be restricted by the capacity of a circulating pump or the like, so that it is difficult to obtain a high-viscosity (high-concentration) polymer liquid.
In order to conduct the high-pressure reaction by introducing a supercritical fluid of a high-pressure monomer into the tubular reactor as described above, various apparatuses, such as a huge and expensive compression apparatus to compress the monomer, an apparatus to keep the high pressure and a safety apparatus, are necessary. Further, the reaction using the supercritical fluid (liquid) is often carried out at relatively low temperatures, and thus the heat of reaction is hardly removed in spite of a wide heat-transfer area of the reactor.
In the liquid phase polymerization process, further, the resulting polymer must be separated from the solvent after the polymerization as described above.
In view of the foregoing conventional techniques, the present inventor has studied polymerization apparatuses and polymerization processes which can perform polymerization with excellent thermal efficiency and small power energy, which can produce various polymers with reduced restrictions on their properties such as viscosities and melting points, and which can simplify the procedure of removing a solvent from the resulting polymer after the polymerization. As a result, the present inventor has found that the above conditions can be satisfied with a polymerization process using a separated flow, which comprises feeding a monomer as a raw material, a polymerization catalyst, and optionally, an inert medium to a tubular reactor in a pressurized state; permitting a part of the raw material monomer and the inert medium fed to the reactor to form a gas phase and the remainder to form a liquid phase, so that both of the gas phase and the liquid phase are present in the reactor, wherein said liquid phase may contain a solid, such that a gas-liquid separated flow or a gas-liquid-solid separated flow has the gas phase that is continuous in the direction of flow is formed in the reactor; and polymerizing the raw material monomer while carrying the liquid phase by the gas phase flow, wherein the ratio of a volume flow rate of the liquid phase to a volume flow rate of the gas phase at the outlet of the reactor is 0.00001 to 100,000. Based on the finding, the present invention has been achieved.
It is known that fluids of gas-liquid two phases or fluids of gas-solid-liquid three phases introduced into a tube form a separated flow, as described in literatures (e.g., Gas-Liquid Two Phase Flow Technique Handbook, "1. Flow Regime" ed. by The Japan Society Of Mechanical Engineers, 1989), but any polymerization reaction performed in a tube wherein the separated flow is formed is not known.